1. Field of the Invention
The invention relates generally to manufacture of flexible materials for packaging and the like. More particularly, it relates to a method for manufacturing permeable films.
2. Background Information
In the packaging industry, allowing oxygen to permeate a film or package so as to contact a product contained therein often is desired. For example, a package utilizing a permeable film can permit oxygen to permeate to a fresh red meat product in the package, thereby allowing the meat product to oxygenate (sometimes called blooming). This can enhance consumer appeal, and retail vendors of such meat products have begun to demand this type of capability. Additionally, many types of produce require the presence of oxygen to suppress anaerobic spoilage.
To obtain sufficient permeability, films frequently are treated with mechanical perforating mechanisms. Unfortunately, mechanical perforation is expensive and cannot be accomplished easily after film manufacture or packaging by, for example, retail vendors. Furthermore, providing perforations which are sufficiently small and uniform in size is a not insubstantial challenge using presently available mechanical perforating techniques.
The need remains for an efficient, cost-effective, versatile method of making permeable films.
According to the present invention, a method for making permeable film is provided. The film advantageously can be made permeable before or after packaging, and permeability is provided through small and substantially uniform perforations as desired.
Briefly, the present invention provides a relatively uncomplicated, inexpensive method for making a permeable film. The method involves applying a physical force to a film of a first material that contains particles of a second (different) material which has a higher susceptibility to the physical force than the first material. Application of the physical force affects the second material which acts on the first material so as to form holes, thereby increasing permeability of the film. The second material can be particles or flakes derived from one or more of a metal, carbon black, ferromagnetic material, or the like. The physical force may be one or more of inductive heating, infrared heating, magnetic force, ultrasonic excitation, microwave irradiation, electron beam (e-beam) irradiation, mechanical stretching, or the like.
In another aspect, the present invention provides a method for making a permeable package. The method involves applying a physical force to a package that includes a product and the above-described film. As before, application of the physical force to the package affects the second material which, in turn, acts on the first material so as to form holes which allow the product to be exposed to oxygen through the film. Films treated according to this method can be rendered permeable before or after manufacture of the package through simple application of a physical force such as those described immediately above.